Electronic actuator for an engine protective system



Avg-v 1970 I R.- B. JOHNSON, JR, ET AL 3,524,110

ELECTRONIC ACTUATOR FOR AN ENGINE PROTECTIVE SYSTEM 2 Sheets-Sheet 1Original Filed 0st. 11, 1966 OIL RETURN INVENTORS JOE E. sooowm RALPH a.JOHNSON,JR.

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ATTORNEYS J 1, 1970 R. B. JOHNSON, JR ET AL EBECTBONIC ACTUATOR FOR ANENGINE PROTECTIVE SYSTEM 2 Sheets-Sheet 3 Original Filed Oct. 11. 1966INVENTORS JOE E. GOODWIN RALPH B. JOHNSON JR.

' C Oflm /wn, {Mia/m Malian ATTORNEYS United States Patent 3,524,110ELECTRONIC ACTUATOR FOR AN ENGINE PROTECTIVE SYSTEM Ralph B. Johnson,Jr., and Joe E. Goodwin, Houston, Tex., assignors to SentinelDistributors, Inc., Denver, 0010., a corporation of Delaware Originalapplication Oct. 11, 1966, Ser. No. 585,798, now Patent No. 3,385,278,dated May 28, 1968. Divided and this application Dec. 29, 1967, Ser. No.716,251 Int. Cl. H01h 47 /32; H02j 7/14; H02p 3/00 US. Cl. 317-1485 11Claims ABSTRACT OF THE DISCLOSURE The flow of fuel to an internalcombustion engine is controlled to provide a safety shut down of theengine in response to a malfunction of the engine or an accessory devicedriven by the engine. A solenoid operated valve is connected in the fuelsupply system and has its operating coil adapted to be energized by anelectronic sensing circuit which monitors the operation of the engine orthe accessory device.

This application is a division of US. Ser. No. 585,798, filed Oct. 11,1966, by Ralph B. Johnson, Jr. et al., now Pat. 3,385,278.

The present invention relates to engine protective sys tems and moreparticularly to an electronic actuator adapted for use in engineprotective systems of the type shown and described in US. Pat.3,202,143.

In US. Pat. 3,202,143, there are disclosed pressure and temperatureresponsive engine shut-down devices adapted for automatically shuttingdown internal combustion engines in response to abnormal pressure ortemperature conditions by cutting off the supply of fuel to the engine.This automatic cut-off is effected whenever the pressure of the oillubricating either the engine or a machine driven by the engine fallsbelow a predetermined level or whenever the coolant temperature exceedsa preset maximum.

In many installations, engines are unitized to a compressor and thereare provided a number of normally open safety switches and associatedindicators which are connected to ground the engine magneto when amalfunction occurs and provide a visual indication of the malfunction.The switches are conveniently mounted to a tattle-tale panel throughwhich the ground connection is made. Commercially available panels maycontain any number of safety switches, and panels accommodating up to 22switches are common. Although such systems provide an effective means ofproviding visual indication of a malfunction hence the name oftattle-tale, and grounding the engine magneto, they do not close off thefuel supply to a gas engine, which is still the most desirable way ofsecuring operation in case of an emergency.

The present invention is an improvement over the aforementioned U.S.patent in that the fuel supply to the engine is adapted to be cut offwhen any malfunction occurs and any existing safety switch of atattle-tale panel operates to ground the engine magneto.

The versatility of such a system affords several advantages. By cuttingotf the supply of fuel to the engine as a result of any malfunction ofthe engine or associated driven equipment, post ignition or dieselingcaused by carbon deposits in the engine head, which continue to glowafter the magneto is grounded, is prevented. Also, the compressors orother driven equipment are precluded from restarting the engine and theexplosion hazard is reduced. Gas leaks to the carburetor when the engineis not running are prevented and damage to the valves and other engineparts due to sour gas are minimized.

The principal object of the present invention is to provide a rugged,low cost trouble-free electronic actuator capable of effectivelyprotecting an engine or an enginedriven accessory against damage uponthe occurrence of a malfunction in the system.

Another object of the present invention is to provide an electronicactuator adapted to cut off automatically the supply of fuel to anengine whenever the engine magneto is grounded.

A further object of the invention is to provide a safety shut-downsystem which is capable of reacting positively to excessive water jackettemperature and oil pressure failure or grounding of the magneto to cutoff the supply of fuel to an engine.

Another object of the present invention is to provide a novel actuatingcircuit responsive to the output of an engine driven magneto forcontrolling operation of the engine.

A further object of the present invention is to provide a novel pulsesensitive circuit for actuating a load device.

Still another object of the present invention is to provide a novelr.p.m. sensitive circuit for actuating a load device.

Another object of the present invention is toprovide a novel r.p.m.sensitive circuit for providing a simple and reliable indication on ther.p.m.s of a driven element.

A further object of the present invention is to provide a novel batteryoperated actuating circuit including means for maintaining the batteryconstantly charged.

These and other objects of the invention, including the provision of asafety shut-down system of the character described which can be quicklyand easily installed on any engine or engine-driven unit such as atransmission, torque converter, compressor or the like, and which willoperate reliably after initial installation without adjustment,maintenance or repair over long periods of time, will appear more fullyupon consideration of the detailed disclosure which follows,

To this end, in accordance with one feature of the present invention,there is provided a solid state electronic actuator which is responsiveto the output of an engine magneto and adapted to actuate a solenoiddump valve upon grounding of the magneto. The solenoid valve isconnected in the oil lubricating system and controls actuation of anindependently operable oil pressure fuel cut-off valve which effectscut-off of the supply of fuel to the engine to provide a fast, positiveengine shut-down.

In accordance with another feature of the invention, the electronicactuator is adapted to be pulse or r.p.m. responsive to effect cut-offof the fuel supply whenever the engine falls below a set r.p.m. level orexceeds a set r.p.m. level.

In accordance with another feature of the invention there is provided atrickle charging circuit adapted to maintain the operating battery fullycharged from the in put pulses to the electronic actuator.

Although certain specific embodiments of the invention are described andillustrated in the accompanying drawings, it is to be especiallyunderstood that these drawings are for the purpose of illustration onlyand are not intended to be construed as defining the limits of theinvention, for which latter purpose references should be had to theappended claims.

In the drawings, wherein like reference characters indicate like partsthroughout the several views:

FIG. 1 is a fragmentary, diagrammatic view of the present inventionwherein an internal combustion engine using vapor gas, i.e., naturalvapor gas or butane-propane, is fitted with both oil pressure responsiveand coolant temperature responsive engine shut-down devices and asolenoid valve adapted to be actuated by an electronic actuator inaccordance with the present invention.

FIG. 2 is a schematic diagram of the electronic actuator of the presentinvention which is pulse time sensitive to the engine magneto output;

FIG. '3 is a schematic diagram of the electronic actuator of the presentinvention which is r.p.m. sensitive to the enigne magneto output, andFIG. 4 is a schematic diagram of the electronic actuator of the presentinvention provided with a built-in engine overspeed control; and FIG. 5is a graphical representation of a typical magneto output pulse.

Referring now to FIG. 1 the physical details of well known components ofthe engine protective system, including the engine and accessory drivenequipment, have been omitted for clarity; however, it should be apparentthat the system comprises the usual carburetor C, oil pump 0 and coolingjacket J. An oil pressure control engine shutdown device or valve A anda coolant temperature control shut-down device or valve B are providedin combination with the typical internal combustion engine or primemover.

The detailed construction of valves A and B are fully disclosed in theaforementioned US. Pat. 3,202,143, to which reference may be made.Accordingly, the details of valves A and B will not be herein described.However, it should be noted that when installing the devices on a vaporgas engine, it is preferably that valve A be connected to the intakeside of the fuel pump and mandatory that it be so connected to thepressure side of the oil pump 0. Valve B is simply threaded into atapped hole in the jacket I and connected by suitable hose lines L tothe oil outlet fitting of valve A and a non-pressure oil return openingin the engine block.

For convenience, the safety valves A and B will be referred tohereinafter as the Oil Sentinel and Heat Sentinel, respectively. HeatSentinel B, which is threaded into the cooling jacket I of the engine,as indicated in FIG. 1, may be operable by a fusion type thermal sensingelement (not shown) responsive to temperature variations of the coolantmedium in said jacket, and is adapted to cause a drop in the oilpressure to which Oil Sentinel A is subject, sufficient to effectclosing of the fuel valve whenever the temperature of the coolantexceeds a predetermined value.

Oil Sentinel A is connected to the forced feed lubricating system of theengine with which it is associated, however, it is also adapted forconnection to the lubricating system of an engine driven accessory, suchas, for example, a compressor D illustrated by dashed lines in FIG. 1.The oil pressure responsive Oil Sentinel A includes an internal fuelvalve (not shown) connected in the fuel line H of the engine adapted tobe closed to cut off the supply of fuel to the engine. It should beapparent that the fuel valve is maintained in an open positionpermitting a free flow of fuel from the inlet side, through the valve tothe carburetor, as long as the oil pressure in the lubricating system ofthe engine (or associated driven accessory equipment) is maintained ator above the predetermined valve established for operationof the oilpressure responsive Oil Sentinel A.

As described in US. Pat. 3,202,143, Oil Sentinel A may also have itsfuel valve partially opened by a manual control G when the operating oilpressure is insuflicient to actuate the fuel valve to its full openposition. Such manually operable means are particularly useful when theengine is unitized to a compressor, because it is frequently desirableto run the engine with the compressor disengaged, under which conditionsthe oil pressure in the lubricating system of the compressor would nothold the fuel valve in its open condition and the supply of fuel to theengine would be cut off.

Thus far, there has been described an engine safety shut-down system ofthe type disclosed in the aforementioned US. Pat. 3,202,143, the detailsof which are incorporated herein by reference. In accordance with thepresent invention, there is incorporated on the inlet side 4 of the OilSentinel A, a solenoid valve V adapted to be actuated in response to theoutput of the engine magneto M to cause a drop in oil pressure to whichOil Sentinel A is subject, sufficient to effect closing of the fuelvalve upon any malfunction of the engine or associated driven equipment.

The present invention is particularly adapted for operation in a systemwherein the engine is unitized to a com pressor and there is providedone or more normally open safety switches S mounted to a tattle-talepanel P and adapted to be actuated to ground the magneto M upon theoccurrence of a malfunction. The output of the engine magneto M isconnected to an electronic actuator E arranged to energize the operatingcoil of the solenoid valve V.

Advantageously, actuator E comprises a battery operated solid statecircuit which may be completely potted, if desired, to withstand therigors of vibration and adverse environmental conditions and which maybe suitably mounted at any location. To this end, there is provided anovel battery charging trickle circuit which maintains the battery in acharged condition from the output of the engine magneto so as to avoidthe necessity of frequent battery replacement.

Electrical connections to the actuator are made through a plurality ofexternal terminals 10-14. Terminals 10 and 11 serve to connect thesolenoid operating coil 15 to the actuator circuit through a pair ofconductors 16 and 17. Terminal 12 provides a ground connection to theengine through conductor 18 and terminal 13 provides the connection tothe magneto output through conductor 19 and is also connected to theungrounded side of the normally open tattle-tale switches S. A fifthterminal 14 is provided where it is desired to obtain fuel shut-offwithout magneto grounding. in such an arrangement, terminal 13 isconnected directly to the magneto output and terminal 14 is separatelyconnected to one or more safety switches adapted to be actuated to theirclosed position upon the occurrence of a malfunction in the system.

Referring now to FIG. 2 there is shown schematically an electronicactuator which is adapted to be incorporated into the protective safetyshut-down system of FIG. 1 and which functions in response to the outputof the engine magneto M to control energization of the operating coil 15of solenoid valve V which may be any suitable 3-way, normally opensolenoid valve such as, for example, the commercially available Humphreymodel 250 E-3. Operating coil 15 is electrically connected across asmall battery pack 20 through terminals 10 and 11; however, operatingvoltage to the coil is not applied until closure of a pair of normallyopen relay contacts 21 connected in series with the coil. A diode 45electrically connected across the operating coil 15 may be provided toprevent excessive voltage kick-back.

Battery pack 20 also provides the necessary bias voltage for operationof the actuator which comprises a sensor unit including a sequence orswitching transistor 22, timing transistors 23 and 24 and settransistors 25 and 26 forming a teeter-totter circuit adapted to be set,cycled and returned to its OFF state. In addition, the actuatorcircuitry components that permit the battery to be charged include theoutput of the engine magneto. The trickle charge current is applied tonegative terminal of battery 20 from terminal 13 through seriesconnected re sisters 27, 28 and diode 29 during the negative swing ofthe magneto output (FIG. 5). The return path for the trickle chargecurrent from the positive terminal of battery 20 to ground is throughcollector-emitter junctions of timing transistors 23 and 24 when thecircuit is in the SET state and through diode 30 connected across thecollector emitter junction of transistor 23.

As shown in FIG. 5, the output of the magneto M applied to terminal 13is a damped oscillation, the pulses of which have negative and positiveexcursions below and above a reference point indicated by horizontaldashed line 31. Thus, in operation, only the negative pulses of theengine magneto are passed through diode 29 which has its anode connectedto the positive terminal of battery 20 and its cathode connected to thelower end, as viewed in the drawing, of resistor 28.

The positive pulses of the output of the engine magneto are used to SETthe teeter-totter circuit in such a manner as to prevent a false cycleand are applied through diode 32 to charge the SET capacitor 33connected between the emitter electrode of switching transistor 22 andground. Zener diode 34, connected to ground from the base electrode oftransistor 22, and biasing resistor 35 connected across the base emitterjunction of transistor 22 establish the operating reference points toprevent false operation by allowing 25, 26 to be reversed biased before24 and 23 are turned on.

On engine start-up, a negligible amount of power is taken from thepositive low tension pulses of the engine magneto to charge SETcapacitor 33 directly through resistors 27, 28 and diode 32. Thecharging current to capacitor 33 is applied until the voltage across thecapacitor exceeds the break-down voltage of Zener diode 34. At thispoint, transistor 22 conducts and timing capacitor 36 in the basecircuit of timing transistor 24 is charged through transistor 22 viaconductor 37. Continued positive pulses maintain the charge of SETcapacitor 33 slightly above the Zener voltage and the charge of thetiming capacitor 36 slightly lbelow the Zener voltage, the ditferencebeing approximately equal to the voltage drop across thecollector-emitter junction of transistor 22.

When capacitors 33 and 36 reach their steady state condition, timingtransistors 23 and 24 are held in conduction by a current flow throughresistor 38 and their base-emitter junctions. Resistor 38 is connectedfrom the ungrounded end of capacitor 36 to the base electrode oftransistor 24. The collector electrode of transistor 24 is connected,together with the collector electrode of transistor 23, to the positiveside of battery 20. The emitter electrode of transistor 24 is connectedto the base electrode of transistor 23, and the emitter electrode oftransistor 23 is connected to ground. Biasing resistor 39 sets thereference operating point for the timing transistors.

Also, when capacitors 33 and 36 have both reached their steady statecondition, SET transistors 25 and 26 are maintained non-conducting by areverse voltage developed across the voltage divider network comprisingresistors 40, 41 and diode 42. Advantageously, relay R does not react toshort pulses due to its relatively long actuation time. The anode ofdiode 42 is connected to the ungrounded side of SET capacitor 33 whilethe cathode of diode 42 is connected to one end of resistor 41, theother end of resistor 41 being connected to one end of resistor 40 whichhas its other end returned to the negative side of battery 20.

The junction of resistors 40 and 41 is connected to the base electrodeof transistor 26 which, together with transistor 25, forms a betamultiplier configuration. The junction of resistors 40 and 41 is alsoconnected to ground through diode 43 which limits the reverse voltageapplied to the base of transistor 26. The base-emitter junctions oftransistors 25 and 26 are serially connected to ground, while theircollector electrodes are tied together and connected to the negativeside of battery 20 through the energizing coil 44 of actuating relay R.A protective diode 45 may be provided across the coil to protect againstexcessive voltage kick back.

As hereinbefore described, the normally open contacts 21 of theactuating relay R are arranged in series with the operating coil of thesolenoid valve so that upon removal of the hold-off voltage applied tothe base of the transistor 26, the timing transistors are free toconduct, whereupon coil 44 is energized, contacts 21 closed and coil 15connected across battery for actuation of valve V. Actuation of valve Vcloses the oil lubricating line nel A which, in turn, causes the fuelvalve in the fuel line to be closed and shut oif the fuel supply to theengine.

In operation, either terminals 13 or 14 may be shorted to the ground orthe input signal from the engine-magneto removed. Any of theseconditions serve to remove the sustaining charge from SET capacitor 33and cause the circuit to cycle. When the sustaining charge is removed,SET capacitor 33 which advantageously has much less capacity than timingcapacitor 36, is rapidly discharged through resistor 41, diode 42 anddiode 43. The discharge drives the base junction of transistor 26 tozero potential. Diode 42 prevents any further discharge of capacitor 33and also prevents capacitor 33 from robbing current from the base oftransistor 26. The voltage at the base of transistor 26 is now free toexceed the voltage drop of the base-emitter junctions of the SETtransistors 25 and 26 whereupon these transistors are driven intosaturation from the current drive applied by battery 20 through resistor40, causing coil 44 of the actuating relay to be energized and contacts21 to close.

In the meantime, timing transistors 23 and 24 are being maintained orheld ON by the discharge of capacitor 36 through resistor 38 and thebase-emitter junctions of transistors 23 and 24. The cycle continuesuntil the discharge current from timing capacitor 36 can no longermaintain the timing transistors in the ON condition. The ON time isdependent on the time constant fixed by capacitor 36 and resistor 38which is made relatively long as compared to the time constant ofcapacitor 33 and resistor 41. When timing transistors 23 and 24 areturned OFF, the cycle state is complete and the actuator relay coil 44is deenergized. Contacts 21 are returned to their open condition andsolenoid valve V opens. The unit then assumes the OFF state.

The electronic actuator or sensor unit is automatically set as theengine comes up to speed in 5 to 15 seconds. If the engine magneto isshorted (grounded) by any of the tattle-tale panel safety switches so asto remove the output pulses applied to the sensor unit, the circuit willcycle to actuate the solenoid valve V which automatically closes the OilSentinel fuel valve. A fast, positive fuel and engine shut-off is thusprovided (3-5 seconds) and, in addition, the tattle-tale panel P, asusual, will indicate the malfunction which caused the shut-down.

Referring now to FIG. 3, there is shown an alternate embodiment of anelectronic actuator, similar in reaction to that shown in FIG. 2, butwhich is modified slightly to eliminate problems which may occur onengine startup by eliminating the simultaneous charging of capacitors 33and 36 of the SET circuit of the teeter-totter sensor unit of FIG. 2 andrequiring the timing capacitor 68 (FIG. 3) to be discharged at a latertime by the conduction of transistor 65 which is actuated by the r.p.m.sensitive input circuit rather than a pulse time sensitive circuit. Thetime that solenoid 15 is held on during the charge of capacitor 68 isindependent of the input pulse time relationship thereby allowing theelectronic actuator to be automatically SET as the engine reaches afixed r.p.m. such as, for example, 100 r.p.m.

The electronic actuator, for convenience, may be broken down into 4elements, a trickle charging circuit, an r.p.m. sensitive timingcircuit, a set circuit and the actuating circuit, and components havingsimilar operating functions to like components of FIG. 2 have beensimilarly identified.

The trickle charging circuit comprises resistor 27 connected betweenterminals 13 and 14 and diodes 50 and 51 which are serially connected tobattery 20. The anode of diode 50 is connected to the ungrounded end ofSET capacitor 33 and to the cathode of diode 51 which has its anodeconnected to the negative side of the battery 20. The input pulses fromthe engine magneto that charge the battery are applied to the cathode ofdiode 50 through resistor 27 and through diode 51 to the battery 20causing a drop in oil pressure and actuation of Oil Senti- It should beapparent that the charging circuit and the input end of the r.p.m.sensitive circuit have a number of common elements, primarily resistor27, diodes 50 and 51 and capacitor 33. The diodes 50 and 51, withresistor 27, perform a current limiting function as well as a rectifyingfunction required for battery charging. The SET capacitor 33 is chargedto the battery voltage less the forward voltage drop of inhibiting diode51 and any negative pulse from the damped pulse train of the magnetooutput applied at terminal 13 that is in excess of the voltage acrossthe capacitor will serve to charge the battery.

The voltage across SET capacitor 33 also appears across the parallelconnected voltage divider comprising resistors 52 and 53. The junctionof resistors 52 and 53 is connected to the base electrode of thesequence or switching transistor 22 which forms the switching elementfor the rpm. circuit. The emitter electrode of transistor 22 isgrounded, while the collector electrode is connected to the negativeside of battery through resistor 54. Diode 55 is connected between thebase electrode and ground protects the base-emitter junction oftransistor from being reverse biased. Diode 55 may alternatively beconnected from terminal 14 to ground as indicated by the dashed lines.

Upon charging of capacitor 33 the voltage at the junction of theparallel connected voltage divider is applied as a trigger input to thebase electrode of transistor 22. Advantageously, the charge rate ofcapacitor 33, dependent on the charging circuit formed by resistor 27,is large in comparison to its discharge rate dependent on resistor 52.In this manner, transistor 22 is held on for the damped portion of themagneto pulse train input and only one operating pulse is received perdamped pulse train input from the magneto to the rpm. sensitive circuit.

The remainder of the rpm. sensitive circuit consists of capacitor 56,resistor 57, diodes 58 and 59, capacitor 60 and serially connectedresistors 61 and 62. Capacitor 56 and resistor 57 are serially connectedfrom the collector electrode of transistor 22 to the common junction ofthe cathode of diode 58 and anode of diode 59. The cathode of diode 59is grounded, while the anode of diode 58 is joined to the parallelconnected capacitor 60 and resistors 61, 62.

The output of the rpm. sensitive circuit is taken from the junction 63of resistors 61 and 62 and applied through diode 64 to the baseelectrode of the SET transistor 65. Transistor 65 is arranged in acommon emitter circuit configuration and has its base electrodeconnected to ground through temperature stabilizing resistor 66 and itscollector electrode connected to the negative side of battery 20 throughresistor 67. The emitter electrode is grounded directly.

The output of the SET circuit is taken from the collector electrode oftransistor 65 and coupled to the actuator circuit which comprisescapacitor 68, resistors 69 and 70, diode 71, transistors and 26 and theactuating relay R which includes the energizing coil 44 and normallyopen contacts 21.

In operation, when transistor 22 is turned on, a discharge path isestablished for capacitor 56 through resistor 57, diode 59 andtransistor 22. At the end of an output pulse train from the enginemagneto, transistor 22 is turned off allowing capacitor 60 to be chargedthrough diode 58, and resistor 57, capacitor 56 and resistor 54. Thedischarge path of capacitor 60 is through the voltage divider comprisingresistors 61 and 62. The discharge rate of capacitor 60 is made muchless than the charge rate so that capacitor 60 accumulates a charge andthe voltage across capacitor 60 is proportional to the r.p.m. of theengine.

When the engine speed exceeds 100 rpm. the voltage developed acrossresistor '62 due to the discharge of capacitor 60 exceeds the baseemitter voltage threshold of transistor 65 and the transistor is turnedON. Switching 8 of transistor 65 to its ON state establishes a dischargepath for capacitor 68 which may be traced through resistor 69, diode 71and transistor 65. Transistor 65 will maintain capacitor 68 dischargedas long as the engine rpm. is in excess of 100. The circuit is thenconsidered to be in the SET state.

When the engine speed drops below rpm. or terminals 13 or 14 areconnected to ground through an external switch, the voltage developed at63 across resistor 62 is no longer sutficient to maintain transistor 65in conduction and the transistor is switched off. When transistor 65 isoff, capacitor 63 is charged through resistor 67 and the base emitterbeta multiplier circuit of transistors 25 and 26 which go intosaturation causing the operating coil 44 to be energized. Energizationof coil 44 causes contacts 21 to close, thus activating the coil 15 ofsolenoid valve V as hereinbefore described. The unit is then consideredto be in the CYCLE state.

As should be apparent, the cycle time is dependent upon the chargingrate of capacitor 68, providing the current flowing into the betamultiplier 25 and 26 is suflicient to hold transistors 25 and 26 insaturation. When the charging current has dissipated, transistors 25 and26 come out of saturation, relay R and solenoid valve V are deenergizedand the unit assumes the OFF state.

Referring now to FIG. 4, there is illustrated another embodiment of theelectronic actuator which is similar to that shown in FIGS. 2 and 3, butwhich is modified slightly to separate low speed detection ofapproximately 100 rpm. and high speed detection ranging from 900 to 1500r.p.m. and which also can be used to provide a linear indication ofengine r.p.m.

The modified r.p.m. sensor circuit consists of an additional transistor72 and its associated elements including emitter resistor 73 and aparallel RC network 74 comprising capacitor 75 and serially connectedresistors 76, 77 and 7 8.

The input transistor 22 of the rpm. circuit operates as hereinbeforedescribed and the positive pulse from the magneto output applied atterminal 13 charges capacitor 33 to a voltage equal to the batterypotential through resistor 27 and diode 50. The voltage across capacitor33 likewise appears across the voltage divider comprising resistors 52and 53, and the voltage at the junction of resistors 52 and 53 turnstransistor 22 ON. When transistor 22 is turned ON, the charge stored incapacitor 56 (FIG. 4) is transferred through a high impedance sourcecomprising the collector of transistor 72 and the emitter resistor 73into the RC network 74 thereby eliminating an interaction between thecharging circuit, capacitor 56 and resistor 73, and the RC network 74.This makes the voltage across the RC network 74 linear with respect tothe number and amplitude of the current pulses and allows the RC networkto be referenced to the positive terminal of the battery (FIG. 4).

Th magnitude of the voltage across the RC network depends upon theimpedance of the RC network and the rate of charge supplied to the RCnetwork by capacitor 56. The RC network voltage therefore is directlyproportional to the rpm. of the engine. Thus, it should be apparent,that a suitable indicating device 79 such as, for example, a meter maybe connected to the collector circuit of transistor 72 to provide alinear indication of engine r.p.m.

As hereinbefore described, the purpose of the voltage developed acrossthe capacitor 33 is to maintain transistor 72 ON for the limit of theinput pulse train of the engine magneto output and to provide sufiicienttime to discharge capacitor 56. A single discharge of capacitor 56 persingle pulse train of the magneto is thus effected. When transistor 22turns off, capacitor 56 is charged. The charging circuit may be tracedfrom the negative side of battery 20 through resistor 54, capacitor 56and diode 59 which is returned to the positive side of the battery.

The r.p.m. sensitive circuit of FIG. 4 differs from the r.p.m. circuitof FIG. 3 through the addition of transistor 72 and its associatedelements in addition to having transistors of an opposite conductivitytype. The type of transistor used, NPN or PNP depends upon the polarityof the battery and diodes and as a practical matter is governed by theavailability of components. Formerly, the charge transfer from capacitor56 to the RC network was equal to the difference in potential whichexisted between capacitors 56 and 60 (FIG. 3). Presently, by theaddition of transistor 72, the charge supplied is equal to the capacityof capacitor 56 times the battery potential, less the diode voltage dropof the diode 59. This is so regardless of the potential appearing acrosscapacitor 75. This improvement allows the use of substantially theentire range of the battery potential for a linear indication of enginer.p.m. As hereinbefore mentioned, a meter 79 could be connected from thecollector of transistor 72 to the positive side of the battery (negativegrounded) to provide a visual indication of engine r.p.m. Of course,other suitable indicators may also be used.

Two outputs are provided from the r.p.m. sensitive circuit. The firstoutput corresponds to the higher r.p.m. of the engine, approximately 900to 1500 r.p.m., and is taken from the collector electrode of transistor72 and applied to the emitter electrode of high speed trigger transistortrigger 80. The second output corresponds to the lower r.p.m. of theengine, approximately 100 r.p.m., and is taken from the junction ofresistors 76 and 77 and applied to the base electrode of the low speedtransistor trigger 81.

The high speed or overspeed trigger circuit comprises transistor 80 andresistors 77 and 78 of the RC network 74. The low speed trigger circuitcomprises transistor 81 and resistor 76 and capacitor 75 of the RCnetwork 74. A tap 82 is provided on battery 20 and connected to the baseof transistor 80 to provide a reference voltage therefor. Likewise, tap83 on battery 20 is connected to the emitter electrode of transistor 81to provide a reference voltage therefor. The use of the tapped batteryprovides a curve matching technique which permits separation of lowspeed detection of approximately 100 r.p.m. from high speed detectionranging from approximately 900 to 1500 r.p.m.

In order to accomplish this two-speed curve match, the initial impedanceof the RC network is made such that a ten or 20 r.p.m. difference willhave a great effect on the output voltage of the RC network. On theother hand, the high speed RC network is advantageously madeapproximately ten times smaller so that the total range does not exceedthe supply voltage. Accordingly, resistor 76 will have a value which isvery large with respect to the total value of resistors 77 and 78, i.e.,greater than 10 times the sum of resistors 77 and 78.

In this manner, the small average currents at the 100 r.p.m. level willallow the voltage across the RC network 74 to be equal to the voltage ofthe battery cell 84 plus the baseemitter drop of low speed transistor81. When 100 r.p.m. is exceeded, transistor 81 conducts heavily andresistor 76 is effectively shorted by the base-emitter of the transistorand a discharge path is established for capacitor 85 through diode 86,the battery cell 84 and the collector-emitter junction of transistor 81.The low speed trigger transistor is thus SET to trigger transistors 25and 26 upon either the loss of input pulses or the reduction of inputpulses below the 100 r.p.m. level.

Diode 86 provides a low impedance for the discharge of capacitor 85 andis connected from one end of the capacitor to the positive side ofbattery 20 or, alternatively, to the emitter of transistor 81. The otherend of capacitor 85 is connected to the junction of the collectorelectrode of transistor 81 with the resistor 87 connected to ground.Resistor 87 provides a current limiting element for the charge ofcapacitor 85 or the trigger current to the base electrode of transistor26. Diode 88 connected between the junction of capacitor 85 and diode 86and the common terminal point of the base electrode of transistor 26 andcollector electrode of transistor provides a gate so that drivingcurrent supplied by transistor 80 is not shunted by a reverse chargingof capacitor which would delay triggering of transistors 25, 26.However, diode 88 could be eliminated so long as capacitor 85 is not anelectrolytic capacitor. Also, diode 86 could be eliminated at theexpense of a longer SET time allowing capacitor '85 to be dischargedthrough the temperature stabilizing resistor 89 connected from thesupply bus to the base electrode of transistor 26. Also, a fasterreaction time can be realized by connecting the anode of diode 51directly to terminal 14. Thus, it should be apparent that the variousconfigurations of certain elements of the circuit can be changed to varyrecovery time or reaction time without departing from the inventiveconcept.

As hereinbefore described, resistor 76 is effectively shorted by thebase-emitter junction of low speed trigger transistor 81 as long as theinput pulses from the engine magneto applied to terminal 13 correspondto an excess of 100 r.p.m. of the engine. With resistor 76 effectivelyshorted, the impedance of the RC network is substantially equal to thesum of the resistance of resistors 77 and 78. Since this sum ispredeterminedly set to be at about or less of the resistance of resistor76, relative increases in voltage across the RC network 74 will beproportioned to hundreds of r.p.m. rather than tens of r.p.m. Theabsolute ratio is dependent on the setting of resistor 78 which is apotentiometer whose resistance in the circuit is varied by adjustment ofarm which, in the preferred embodiment, is chosen to allow a speed rangedetection from 900 to 1500 r.p.m. The voltage across the RC networkincreases linearly with an increasing r.p.m. of the engine up toapproximately full battery voltage. Where the RC network voltage exceedsthe reverse bias applied to the transistor 81 from tap 83 and batterycell 84 plus the base-emitter drop of transistor 81 then the excessoutput current of the r.p.m. circuit is directed from the collectorelectrode of transistor 81 to the high impedance base electrode oftransistor 26 which is the first element of the time delay circuitformed by the beta multiplier comprising transistors 25 and 26.

The circuit configuration is similar to that of FIG. 3 and its operationis for all practical purposes the same. In FIG. 3, RC elements 68 and 69are utilized to trigger the beta multiplier for a fixed period such as,for example, one minute. In FIG. 4, capacitor 85, which corresponds tocapacitor 68, is made a smaller value and thereby of lower leakage thancapacitor 68, FIG. 3, and a holding circuit comprising resistor 91 andcapacitor 92, of a much larger value, is provided. Resistor 91 isconnected from the base of electrode of transistor 26 in series withcapacitor 92 which has its free end connected to the terminal 11 and oneside of normally open contact 21 so that capacitor 92 is not chargeduntil coil 44 is energized.

In operation, assuming there is a signal length sufficient to causeenergization of the coil 44, the input current supplied to the baseelectrode of transistor 26 by the action of transistor 81 and capacitor85, or by the action of transistor 80, causes transistors 25 and 26 tosaturate, energizing coil 44 of relay R. This causes contacts 21 toclose allowing capacitor 92 to charge through resistor 91 and providesan additional driving current to the base electrode of transistor 26.The charging current in itself is sufficient to hold transistor 25 ONfor the fixed period which may be approximately one minute. The delaycircuit is therefore driven ON and is held ON until the capacitor 92 ischarged. As capacitor 92 approaches full charge, the holding current isreduced and transistor 25 turns OFF, deenergizing coil 44 and openingcontacts 21. Capacitor 92 then discharges through coil 15 of thesolenoid valve and series connected diode element 93 and resistor 94. Ifdesired, diode 45 and resistor 93 may be eliminated so that diode 94provides kick-back protection 1 1 allowing the inductive kick to bedischarged through capacitor 92 and diode 94.

The battery trickle charge circuit is similar to that of FIGS. 2 and 3and consists of resistor 27 and diodes 50 and 51, with diode 50preventing the battery from operating transistor 22. When the voltagepulses of the magneto exceed the battery voltage, as charging current issupplied to the battery, the current is limited to a trickle charge bythe value of resistor 27. Diode 55 provides a low impedance path fornegative cycles of the magnetos output voltage pulses which appearacross capacitor 33 during normal operation (FIG. 4).

It may also be placed as shown by the dotted lines (FIG. 3), but is moreeffective than the position illustrated in FIG. 4, due to the impedanceratios of the added reversed section due to the impedance ratios of theadded reverse condition of diode 50 in FIG. 4, so that the average DCcurrent flowing in the magneto is extremely small.

Thus there has been shown and described several variations of anactuator circuit adapted to be incorporated in an engine protectivesystem to effect engine shutdown by cutting off the fuel supply to theengine. The actuator also provides a convenient circuit for speeddetection and for linearly indicating r.p.m. independent of its functionin a protective system. It will be readily apparent to those skilled inthe art that various modifications may be made without departing fromthe inventive concept. It is therefore intended by the appended claimsto cover all such modifications which fall within the full scope of theinvention.

What is claimed is:

1. Apparatus for actuating a load device comprising a battery operatedcontrol circuit, said control circuit having an OFF state an a SETstate, input means for applying to said control circuit an input signalcomprising a damped pulse train for switching said control circuit fromsaid OFF state to said SET state and maintaining said control circuit insaid SE state upon the continued presence of said input signal, meansfor cycling said control circuit while in said SET state in response toa predetermined change in said input signal to cause said controlcircuit to be switched from its SET state to its OFF state, a relayhaving an energizing coil and a pair of normally open contacts, saidenergizing coil being connected to said control circuit and adapted tobe energized therefrom upon cycling thereof to cause said contacts toclose, a normally deenergized load device remotely located from saidcontrol circuit and adapted to be electrically connected to the batteryof said control circuit for energization of said load device and meansserially connecting said pair of contacts between said load device andsaid battery such that said load device is energized upon cycling ofsaid control circuit.

2. Apparatus for actuating a load device as set forth in claim 1 furtherincluding circuit means connecting the battery to said input means forapplying to said battery a trickle charge current from the input signalto maintain said battery in a charged condition.

3. Apparatus for actuating a load device as set forth in claim 1 whereinsaid control circuit comprises at least a first transistor, a secondtransistor and a third transistor, each transistor being normally biasedOFF, means connecting said first transistor to said input means to causesaid first transistor to be switched ON by said input signal, meansconecting second transistor to said first transistor for causing saidsecond transistor to be driven ON upon switching of said firsttransistor, said first and second transistors being maintained ON uponthe continued presence of said input signal, said third transistoradapted to be maintained OFF while said first and said secondtransistors are ON thereby establishing the SET state of said controlcircuit, means connecting said third transistor to said secondtransistor for causing said third transistor to be driven ON toestablish the cycling state of said control circuit while said thirdtransistor is driven ON in response to turning OFF of said first andsaid second transistors and said energizing coil of said relay beingconnected to said third transistor and adapted to be energized when saidthird transistor is driven ON.

4. Apparatus for actuating a load device as set forth in claim 3 whereinsaid input means comprises a voltage divider including a SET capacitorand a timing capacitor, said capacitors being serially connected, saidSET capacitor being connected to said first transistor and adapted to becharged from said input signal to cause said first transistor to bedriven ON, said timing capacitor being connected to said secondtransistor and adapted to be charged upon switching ON of said firsttransistor to cause said transistor to be driven ON and said SET andtiming capacitors being adapted to be discharged in responses to apredetermined change in the input signal to cause said control circuitto cycle.

5. Apparatus for actuating a load device as set forth in claim 4including circuit means connecting said SET capacitor to said thirdtransistor forming a discharge circuit for said SET capacitor such thatthe discharge of said SET capacitor causes said third transistor to bedriven ON, means forming a discharge circuit for said timing capacitorthrough said second transistor to maintain said second transistor ON,the discharge time of said timing capacitor being greater than thedischarge time of said SET capacitor whereby the coil of said relay isenergized for a predetermined period of time dependent on the dis chargetime of said timing capacitor.

6. Apparatus as set forth in claim 3 wherein said means connecting saidfirst transistor to said input means comprises a pulse sensitive circuitwhereby said control circuit is SET upon the presence of a pulse signalfrom said damped pulse train and cycled upon the absence of said inputsignal.

7. Apparatus as set forth in claim 3 wherein said means connecting saidfirst transistor to said input means comprises a frequency sensitivecircuit whereby said control circuit is responsive to the frequency ofpulses of the input signal.

8. Apparatus as set forth in claim 3 wherein said input means comprisesa voltage divider including a SET capacitor and a pair of seriallyconnected resistors connected in parallel with said SET capacitor, saidresistors forming a discharge circuit for SET capacitor, meansconnecting the junction of said resistors to said first transistor forapplying thereto a trigger input to cause said transistor to be switchedON, said SET capacitor adapted to be charged from said input signal, thecharge rate of said SET capacitor being large in comparison to itsdischarge rate such that said first transistor is switched ON by oneoperating pulse of the received damped pulse train.

9. Apparatus as set forth in claim 8 wherein said means connecting saidsecond transistor to said first transistor includes a capacitor adaptedto be charged when said first transistor is OFF and discharged when saidfirst transistor is switched ON for causing said second transistor to beswitched ON and maintained ON thereby establishing the SET state of saidcontrol circuit so long as the input signal exceeds a predeterminedfrequency.

10. Apparatus as set forth in claim 7 including an engine driven memberfor providing said input signal,

said input signal corresponding to the r.p.m. of the driven member andfurther including means connected to the output of said first transistorfor providing a linear indication of the r.p.m. of the driven member.

11. Apparatus as set forth in claim 10 wherein said means connected tothe output of said first transistor comprises a first r.p.m. sensitivecircuit for providing a first output signal corresponding to a low speedcondition of the driven member of approximately r.p.m. and a secondr.p.m. sensitive circuit for providing a second output signalcorresponding to a high speed condition ofthe driven member ofapproximately 900 r.p.m. and greater and means for applying said firstsignal and said second signal to said second transistor to allow cycling3,406,775 10/1968 Magnuski 180--105 of said control circuit upon eitherthe reduction of r.p.m 2,934,703 4/1960 Cohen 324-70 of the drivenmember below the said low speed condition 2,294,152 8/ 1942 Yates et a1123-198 or the increase in r.p.m. of the driven member above the3,202,743 8/1965 Goodwin 123-41.15

said high speed condition. 5

LEE T. HIX, Primary Exammer References cued C. R. YATES, AssistantExaminer UNITED STATES PATENTS U.S. Cl. X.L. 2,941,120 6/1960 Harman etal. 317-5 29040; 320 s

